Lecture 7 - Long-term potentiation, Long-term depression, NMDA and AMPA receptors Flashcards
How does Hebb’s cell assembly and memory storage occur?
External stimulus
Activation of the cell assembly by a stimulus
Reverberating activity continues activation after the stimulus is removed
Hebbian modification strengthens the reciprocal connections between neurons that are active at the same time
How does recall of perceptual memory occur in Hebb’s cell assembly?
The strengthened connections of the cell assembly contain the engram for the stimulus
After learning, partial activation of the assembly leads to activation of the entire representation of the stimulus.
How does Hebb describe the organisation of behaviour?
“When an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth processes or metabolic change takes place in one or both cells such that A’s efficiency, as one of cells firing B, is increased’
What is Hebb’s learning rule?
- Correlated pre- and postsynaptic activities cause synapse strengthening/stabilisation
- Uncorrelated pre- and postsynaptic activities cause synapse weakening/ elimination.
“Cells that fire together wire together”
What is long-term potentiation?
Long-Term Potentiation (LTP) : persistent increase in synaptic efficacy after a brief tetanic stimulation of afferent pathways.
-Bliss & Lomo in 1973
What is long-term depression?
Long-Term Depression (LTD) : persistent decrease in synaptic efficacy after a brief episode of low-frequency stimulation (LFS).
-Dunwiddie & Lynch in 1978
What is field EPSP?
Field excitatory post synaptic potential
Are AMPA and NMDA ionotropic or metabotropic?
What does NMDA activate in LTP and LTD?
AMPA - ionotropic, allows Na+
NMDA - ionotropic, allows Ca2+
LTP - activates kinases, phosphorylate AMPA receptors
LTD - activates phosphatases, dephosphorylate AMPA receptors
How are NMDA receptors activated?
High frequency stimulation - NMDA receptors must bind glutamate and experience a depolarisation big enough to remove Mg2+ ions from the channel (voltage-dependent blockade).
How does presynaptic regulation by postsynaptic cell occur?
Postsynaptic cell releases nitric oxide, regulating probability of glutamate release in presynaptic cell
How do dendritic spines undergo structural remodelling after LTP and LTD?
LTP - spine growth
LTD - spine retraction
Size of spine head increases in LTP, decreases in LTD
Structural plasticity is bidirectional and related to synaptic strength.
How does number of AMPA receptors change with LTP?
Number of AMPA receptors increase after LTP
Why LTP is considered as a model for memory?
Memory and LTP are input specific
Memory and LTP uses similar molecular pathways
Most of the drugs that inhibits memory also inhibits LTP
LTP like process occurs during learning
Memory and LTP are associative
What is coincidence detection by an NMDA receptor?
Two things need to happen:
Glutamate released by presynaptic cell
Membrane depolarisation by Na+
What are the many theories for LTP?
Pre-synaptic and post-synaptic
Pre-synaptic=Altered
-Neurotransmitter amount in vesicles
-Number of vesicles released
-Kinetics of release
-Glutamate reuptake
-Probability of vesicle fusion
Post-synaptic=Altered
-Number of AMPA receptors
-Insertion of AMPA receptors
-Ion flow through AMPA channels
-Membrane electrical properties
Additional possibilities include changes in number of total synaptic connections between two cells
